1. Field of the Invention
The present invention relates to a direct type liquid crystal display device and a method of driving the same, and more particularly, to an invention for enhancing the brightness uniformity of the direct type liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device is a display device having advantages such as compactness, light weight and low power consumption, and used for a wall mounted television as well as a monitor of the computer, and the demand has been continuously increased.
Such a liquid crystal display device is a light receiving device for controlling the amount of light received from the outside to display an image, and thus requires a separate light source.
Here, the liquid crystal display device may be divided into an edge type and a direct type.
Of them, the direct type liquid crystal display device has high light use rate and easy handling characteristics and does not have a limit in the size of the display surface, and thus has been widely used for large-sized liquid crystal display devices with a size of more than 30 inches.
For the light source of the direct type backlight assembly, cold cathode fluorescent lamp (CCFL) and external electrode fluorescent lamp (EEFL) are mainly used for the light source of the direct type backlight assembly, but in recent years, light emitting diodes have been also increasingly used.
Hereinafter, a liquid crystal display device according to the related art will be described with reference to the drawing.
FIG. 1 is a cross-sectional view illustrating a direct type liquid crystal display device according to the related art.
The liquid crystal display device is largely divided into a liquid crystal panel 10, a backlight unit (not shown), and a driving circuit unit (not shown).
The liquid crystal panel 10 displays an image on a front surface thereof, and the backlight unit (not shown) performs the role of emitting light, and the driving circuit unit performs the role of driving the backlight unit (not shown) and liquid crystal panel 10. In this case, an upper surface edge of the liquid crystal panel 10 is protected by a top cover (not shown), and the liquid crystal panel 10 is supported by a guide panel 30 disposed at the edge, and the backlight unit is protected by a cover bottom 40 at a lower side.
Here, the backlight unit may include light-emitting diodes (LEDs) 21, a printed circuit board (PCB) 22, a reflective plate 23, and a plurality of optical sheets 24.
The LEDs 21 emit light as a semiconductor emission element. Furthermore, the printed circuit board 22 is accommodated into an upper surface of the cover bottom 40 to operate the LEDs 21, and wiring for driving the LEDs 21 is disposed at a front surface thereof. At this time, the LEDs 21 are disposed at a front surface of the printed circuit board 22 to emit light toward the front.
However, the emission direction of the LEDs 21 may be irregular to emit light to the lateral surface thereof, and reflected within the cover bottom 40, thus generating light which is not directed toward the front disposed with the liquid crystal panel 10.
Accordingly, the reflective plate 23 is disposed at an upper surface of the printed circuit board 22 to reflect the light and scan it to the liquid crystal panel 10. The reflective plate 23 may include an opening area for disposing the LEDs 21, and thus may be fastened to the printed circuit board 22 in such a way that it is placed from an upper surface of the printed circuit board 22 mounted with the LEDs 21 to a lower surface thereof.
Furthermore, the plurality of optical sheets 24 diffuse and condense light directed from the LEDs 21 to the liquid crystal panel 10 to enhance and equalized the illumination. The optical sheets 24 may be comprised of a diffuser sheet, a prism sheet, a protector sheet, and the like.
On the other hand, the liquid crystal display device may vary the brightness of the backlight according to the user's input. In this case, a control signal may be received at the backlight driving unit for driving the backlight by an external signal according to the user's input, and the control signal collectively controls all the LEDs 21 to change the brightness.
However, light directed toward a side wall surface of the cover bottom 40 among the light emitted from the LEDs 21 disposed at the edge may be absorbed into the cover bottom 40. For example, the LEDs 21 disposed at the outer edge in FIG. 1 may include light {circle around (1)}, and the light {circle around (1)} may be absorbed toward the cover bottom 40. However, the LEDs 21 disposed at the central portion may include the form of light {circle around (2)}, and almost all light is incident to the front diffuser sheet.
Accordingly, almost all light emitted from the LEDs 21 disposed at the central portion of the backlight is transmitted toward the front whereas part of the light emitted from the LEDs 21 disposed at the outer edge is transmitted toward the front, and thus the brightness of the backlight may be not uniform over the entire region. In other words, it is observed that the brightness of the backlight in the outer region is lower than that in the central region.
As a result, brightness uniformity in the liquid crystal display device may be deteriorated, and since the brightness uniformity is one of key factors in determining quality, such deterioration of uniformity characteristics may not allow the user to view clear and uniform images.